I'm in a streak of bad luck! How can I change my karma?

We all go through periods of adversity, just as we all go through periods of happiness. Nobody wants distress, but it comes anyway. And happiness also comes in its own time. We can't demand to be happy or mechanically stop distress from arriving on our doorstep.

What we can do is try to rise above it all by making some endeavor in Krishna consciousness. A Krishna conscious person can be happy, no matter what the external circumstances, because his happiness isn't dependent on karmic enjoyment.